I used to have SSMS 2008 R2 installed plus the RedGate Developer Bundle. In SSMS, I could right-click a database in the Object Explorer pane, and I'd have an option to do a Data Compare. This would open a window within SSMS and I could drag & drop another database into this window to specify the target database.

I re-paved my machine and am now using SSMS 2012, again with the Developer Bundle. However the option for Data Compare (and Schema Compare) are missing from the right-click/context menu in the Object Explorer. I've tried repairing the installs for Data & Schema Compare, but this didn't change anything.